The present invention relates to an improvement in the production of continuous metal filaments of indefinite length which are normally wound on spools. More specifically, for the purposes of the invention, filament is herein used to represent a slender body whose transverse dimensions are much less than its length. In the present context, the filaments may be ribbons, sheets, wires or irregular cross-sections.
During recent years, researchers developed various methods directed to the formation of metal filaments which avoid the inherent difficulties of previous casting and rolling techniques. These methods include, for example, melt extraction and chill block spinning.
Melt extraction connotes a process wherein a cold quenching wheel rotates at high velocity in "kissing", i.e. skimming, contact with a liquid metal surface. The molten metal wetting the wheel is carried up out of the molten bath, where it solidifies and thereby shrinks away from the wheel and is flung off by centrifugal action. The melt extraction techniques discussed herein are to be distinguished from other extraction methods such as those described in U.S. Pat. No. 1,025,848 to Wagner and U.S. Pat. No. 2,074,812 to Sendzimer, which primarily employ a casting technique in which the cold wheel is substantially immersed in the liquid metal and in which the rotational velocity of the wheel is appreciably lower than in the melt extraction.
Chill block spinning is exemplified by U.S. Pat. No. 905,758 to Strange and Pim, U.S. Pat. No. 2,825,108 to Pond, U.S. Pat. No. 2,886,866 to Wade, and U.S. Pat. No. 2,899,728 to Gibbons. In this process, a free jet of molten material is impinged upon a moving chilled quenching surface, preferably a rotating wheel. The molten jet is solidified in the form of a ribbon or sheet and is flung away from the rotating chill surface by centrifugal action.
One important disadvantage in the melt extraction and chill block spinning processes as presently employed is that they produce long, but not genuinely continuous filaments. The flinging action which removes the filament from the wheel induces an oscillating or whipping motion in the filament which inevitably causes breakage. Presently filaments are produced with a maximum length of only about 300 meters. Continuous metal filaments in the range of 1,000 to greater than 30,000 meters in length are required for such applications as strapping, springs, filament-wound vessels, aerospace skins and the like.
An additional problem encountered in the melt extraction and chill block spinning process is that of winding the lengths of filament formed. The incorporation of a tension regulated winder or similar collecting device into the system results in a great amount of stress being transmitted back to the solidification zone, a factor which contributes to the breakage of the filaments. Since the "down time" caused by rethreading the filaments onto the winder after breakage is considerable, the metal filaments must be wound in a separate operation. There is obviously a need for a method to produce continuous lengths of metal filaments which can be wound concomitantly with production.